The present invention is with respect to a press having a top platen and a lower platen for making true-to-size pressings of powder material. Such pressings or moldings may for example be gearwheels, pistons of shock-absorbers, synchronizers for automatic transmissions or the like. The pressings are generally made up of iron powder, ferrite powder and ceramic or such like powders.
One press on these lines, which has been used in the assignee's works, had a base plate, a die plate and a lower stamp able to be moved in translation in relation to the base plate and the die plate hydraulically, the base plate and the die plate being parts of a frame structure made up of the die plate and a lower joining plate with pull-rods for connection purposes, the frame structure being joined up by way of a connection piece, able to be moved in translation in relation to the frame structure in the direction of pressing, with the top platen, whereas the lower platen of the press is joined up with the lower joining plate.
In this earlier form of press the base plate took up the lower stamp which had a stepped form and, if desired, was made up of different stamp parts. On easing off or pulling down the lower stamp uneven forces were necessarily produced within the pressing or molding, even if the stamp was made up of a number of stamp parts, such forces being caused by friction between the parts of the die and stamp and the pressing which was to be taken from the mold. Frequently, such forces were a cause of damage to the pressing. A further shortcoming of the earlier press design was that it was hard to make certain of an even density within the pressing.